Correlated quantum machines beyond the standard second law

TL;DR

This paper develops a comprehensive quantum thermodynamics framework that accounts for correlations, revealing new regimes where quantum engines can surpass classical efficiency bounds like Carnot.

Contribution

It derives an exact efficiency formula for quantum engines with correlations and identifies a novel athermal regime where work is extracted from correlations.

Findings

Efficiency can exceed Carnot limit in the athermal regime.

Correlations enable new modes of quantum engine operation.

A unified formalism for correlated quantum machine efficiency.

Abstract

The laws of thermodynamics strongly restrict the performance of thermal machines. Standard thermodynamics, initially developed for uncorrelated macroscopic systems, does not hold for microscopic systems correlated with their environments. We here derive an exact formula for the efficiency of any cyclically driven quantum engine by using generalized laws of quantum thermodynamics that account for all possible correlations between all involved parties, including initial correlations. Furthermore, we demonstrate the existence of two basic modes of engine operation: the usual thermal case, where heat is converted into work, and a novel athermal regime, where work is extracted from entropic resources, such as system-bath correlations. In the latter regime, the efficiency is not bounded by the usual Carnot formula. Our results provide a unified formalism to determine the efficiency of correlated microscopic quantum machines.